Method for fabricating semiconductor device having high withstand voltage transistor

ABSTRACT

The semiconductor device comprises a gate electrode  26  formed on a semiconductor substrate  10,  a source region  45  a having a lightly doped source region  42   a  and a heavily doped source region  44   a , a drain region  45   b  having a lightly doped drain region  42   b  and a heavily doped drain region  44   b,  a first silicide layer  40   c  formed on the source region, a second silicide layer  40   d  formed on the drain region, a first conductor plug  54  connected to the first silcide layer and a second conductor plug  54  connected to the second silicide layer. The heavily doped drain region is formed in the region of the lightly doped region except the peripheral region, and the second silicide layer is formed in the region of the heavily doped drain region except the peripheral region. Thus, the concentration of the electric fields on the drain region can be mitigated when voltages are applied to the drain region. Thus, even with the silicide layer formed on the source/drain region, sufficiently high withstand voltages of the high withstand voltage transistor can be ensured. Furthermore, the drain region alone has the above-described structure, whereby the increase of the source-drain electric resistance can be prevented while high withstand voltages can be ensured.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No. 10/663,705 filed on Sep. 17, 2003 which is now U.S. Pat. No. 6,861,704 and claims priority of Japanese Patent Application No. 2002-273851, filed on Sep. 19, 2002 and U.S. patent application Ser. No. 10/633,705 filed on Sep. 17, 2003, the contents being incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device and a method for fabricating the semiconductor device, more specifically a semiconductor device having high withstand voltage transistors and a method for fabricating the semiconductor device.

In organic EL panels, LCD drivers, ink jet printers, etc., it is noted to mount logic transistors, and high withstand voltage transistors mixedly on and the same substrate for the purpose of their general high operational speed.

A proposed semiconductor device having logic transistors, and high withstand voltage transistors mixed mounted will be explained with reference to FIG. 16. FIG. 16 is a sectional view of the proposed semiconductor device. In FIG. 16, a logic region shown on the left side of the drawing, and a high withstand voltage region is shown on the right side of the drawing.

Element isolation regions 214 for defining element regions 212 a, 212 b are formed on the surface of a semiconductor substrate 210. In the element region 212 a of the logic region 216 a transistor 220 of relatively low withstand voltage having a gate electrode 226, a source region 236 a and a drain region 236 b is formed. The source region 236 a has a lightly doped source region 230 a and a heavily doped source region 234 a. The drain region 236 b has a lightly doped drain region 230 b and a heavily doped drain region 234 b. On the other hand, in the source region 212 b of the high withstand voltage region 218 a relatively high withstand voltage transistor 222 having a gate electrode 226, a source region 245 a and a drain region 245 b is formed. The source region 245 a has a lightly doped source region 242 a and a heavily doped source region 244 a. The drain region 245 b has a lightly doped drain region 242 b and a heavily doped drain region 244 b. An inter-layer insulation film 250 is formed on the semiconductor substrate 210 with the transistors 220, 222 formed on. Conductor plugs 254 are formed in the inter-layer insulation film 250 respectively down to the source regions 236 a, 245 a and the drain regions 236 a, 245 b. An interconnection is formed on the inter-layer insulation film 250, connected to the conductor plugs 254.

The proposed semiconductor device, in which the logic transistors 220, and the high withstand voltage transistors 222 are formed mixedly on one and the same substrate, can contribute to higher operation speed of electronic devices.

Recently, semiconductor devices are increasingly micronized. However, simply micronizing a semiconductor device causes increase a contact resistance and a sheet resistance in the source/drain. As a countermeasure to this, in a logic transistor whose gate length is below, e.g., 0.35 μm, usually a silicide layer is formed on the source/drain region for the purpose of depressing the contact resistance and the sheet resistance in the source/drain.

Another proposed semiconductor device which has the silicide layer formed on the source/drain region will be explained with reference to FIG. 17. FIG. 17 is a sectional view of another proposed semiconductor device.

As shown in FIG. 17, the silicide layer 240 is formed respectively on the heavily doped source regions 234 a, 244 a and the heavily-doped drain regions 234 b, 244 b.

Said another proposed semiconductor device shown in FIG. 17, in which the silicide layer 240 is formed on the source/drain regions, can be micronized while the contact resistance and the sheet resistance in the source/drain are depressed low.

Patent Reference 1 also discloses a semiconductor device having a silicide layer formed on the source/drain regions.

Following references disclose the background art of the present invention.

[Patent Reference 1]

Specification of Japanese Patent Application Unexamined Publication No. Hei 11-126900

[Patent Reference 2]

Specification of Japanese Patent Application Unexamined Publication No. Hei 9-260590

However, the proposed semiconductor device shown in FIG. 16 cannot ensure sufficient withstand voltage of the high withstand voltage transistors. The semiconductor device proposed in Patent Reference 1 cannot ensure sufficiently high withstand voltage.

Here, it can be proposed that a silicide layer is formed on the source/drain diffused layer of the logic transistors only, and in the high withstand voltage transistor, the silicide layer is not formed, but an insulation film covers the source/drain diffused layer thereof. In this case, however, it is difficult to obtain good contact in the high withstand voltage transistor, and the contact resistance and the sheet resistance in the high withstand voltage transistor are very high.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a semiconductor device which can ensure sufficient withstand voltage even in the case that a silicide layer is formed on the source/drain region, and a method for fabricating the semiconductor device.

According to one aspect of the present invention, there is provided a semiconductor device comprising: a gate electrode formed on semiconductor substrate with an insulation film formed therebetween; a source region formed on one side of the gate electrode and having a lightly doped source region and a heavily doped source region having a higher carrier concentration than the lightly doped source region; a drain region formed on the other side of the gate electrode and having a lightly doped drain region and a heavily doped drain region having a higher carrier concentration than the lightly doped drain region; a first silicide layer formed on the source region; a second silicide layer formed on the drain region; a first conductor plug connected to the first silicide layer; and a second conductor plug connected to the second silicide layer, the heavily doped drain region being formed in a region of the lightly doped drain region except a peripheral part thereof, and the second silicide layer being formed in a region of the heavily doped drain region except a peripheral part thereof.

According to another aspect of the present invention, there is provided a method for fabricating a semiconductor device comprising the steps of: forming a gate electrode on a semiconductor substrate with a gate insulation film formed therebetween; implanting a dopant into the semiconductor substrate with the gate electrode as a mask to form a lightly doped source region in the semiconductor substrate on one side of the gate electrode and a lightly doped drain region in the semiconductor substrate on the other side of the gate electrode; forming a sidewall insulation film on the side wall of the gate electrode; implanting a dopant into the semiconductor substrate with a first mask covering a peripheral region of the lightly doped drain region, the gate electrode and the sidewall insulation film as a mask, to form a heavily doped source region in the semiconductor substrate on one side of the gate electrode and a heavily doped drain region in a region of the lightly doped drain region except a peripheral region thereof; and forming a first silicide layer on the heavily doped source region and a second silicide layer in a region of the heavily doped drain region except the peripheral region thereof, with a second mask formed, covering a peripheral region of the heavily doped drain region.

According to the present invention, the heavily doped drain region is formed in the region of the lightly doped drain region except the peripheral region in the drain region of the high withstand voltage transistor, the silicide layer is formed in the region of the heavily doped drain region except the peripheral region, the conductor plug is formed down to the part of the silicide layer except the peripheral part thereof, and the heavily doped drain region 44 is spaced from the element isolation region, whereby when voltages are applied to the drain region, the concentration of the electric fields on the drain region can be mitigated. Thus, according to the present invention, even with the silicide layer formed on the source/drain region, sufficiently high withstand voltages of the high withstand voltage transistor can be ensured. Furthermore, according to the present invention, the drain region alone has the above-described structure, whereby the increase of the source-drain electric resistance can be prevented while high withstand voltages can be ensured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the semiconductor device according to one embodiment of the present invention.

FIGS. 2A and 2B are a sectional view and a plan view of the semiconductor device according to the embodiment of the present invention.

FIGS. 3A and 3B are sectional views of the semiconductor device according to the embodiment in the steps of the method for fabricating the semiconductor device, which show the method (Part 1).

FIGS. 4A and 4B are sectional views of the semiconductor device according to the embodiment in the steps of the method for fabricating the semiconductor device, which show the method (Part 2).

FIGS. 5A and 5B are sectional views of the semiconductor device according to the embodiment in the steps of the method for fabricating the semiconductor device, which show the method (Part 3).

FIGS. 6A and 6B are sectional views of the semiconductor device according to the embodiment in the steps of the method for fabricating the semiconductor device, which show the method (Part 4).

FIGS. 7A and 7B are sectional views of the semiconductor device according to the embodiment in the steps of the method for fabricating the semiconductor device, which show the method (Part 5).

FIGS. 8A and 8B are sectional views of the semiconductor device according to the embodiment in the steps of the method for fabricating the semiconductor device, which show the method (Part 6).

FIGS. 9A and 9B are sectional views of the semiconductor device according to the embodiment in the steps of the method for fabricating the semiconductor device, which show the method (Part 7).

FIGS. 10A and 10B are sectional views of the semiconductor device according to the embodiment in the steps of the method for fabricating the semiconductor device, which show the method (Part 8).

FIGS. 11A and 11B are sectional views of the semiconductor device according to the embodiment in the steps of the method for fabricating the semiconductor device, which show the method (Part 9).

FIGS. 12A and 12B are sectional views of the semiconductor device according to the embodiment in the steps of the method for fabricating the semiconductor device, which show the method (Part 10).

FIGS. 13A and 13B are sectional views of the semiconductor device according to the embodiment in the steps of the method for fabricating the semiconductor device, which show the method (Part 11).

FIGS. 14A and 14B are sectional views of the semiconductor device according to the embodiment in the steps of the method for fabricating the semiconductor device, which show the method (Part 12).

FIG. 15 is a sectional view of a modification of the semiconductor device according to the embodiment of the present invention.

FIG. 16 is a sectional view of the proposed semiconductor device.

FIG. 17 is a sectional view of another proposed semiconductor device.

DETAILED DESCRIPTION OF THE INVENTION

The semiconductor device according to one embodiment of the present invention and the method for fabricating the semiconductor device will be explained with reference to FIGS. 1 to 14B. FIG. 1 is a sectional view of the semiconductor device according to the present embodiment. FIG. 2 are a sectional view and a plan view of the semiconductor device according to the present embodiment. FIGS. 3A to 14B are sectional views of the semiconductor device according to the present embodiment in the steps of the method for fabricating the semiconductor device, which show the method.

(The Semiconductor Device)

First, the semiconductor device according to the present embodiment will be explained with reference to FIGS. 1 to 2B. FIG. 1 shows a transistor in a logic region and a transistor in a high withstand voltage region, which form the semiconductor device according to the present embodiment. The logic region is shown on the left side of the drawing of FIG. 1, and the high withstand voltage region is shown on the right side of the drawing of FIG. 1. FIGS. 2A and 2B show the transistor in the high withstand voltage region forming the semiconductor device according to the present embodiment. FIG. 2A is a sectional view thereof, and the FIG. 2B is a plan view thereof.

As shown in FIG. 1, an element isolation regions 14 for defining element regions 12 a, 12 b are formed on a semiconductor substrate 10.

A logic transistor 20 is formed in the element region 12 a of the logic region 16. The withstand voltage of the logic transistor 20 is relatively low.

In the element region 12 b of the high withstand voltage region 18, a high withstand voltage transistor 22 is formed.

Then, the transistor 20 formed in the logic region 16 will be explained.

As shown in FIG. 1, a gate electrode 26 is formed on the semiconductor substrate 10 with a gate insulation film 24 a formed therebetween. A cap film 28 is formed on the gate electrode 26.

In the semiconductor substrate 10 on both side of the gate electrode 26, a lightly doped region 30, specifically, a lightly doped source region 30 a and a lightly doped drain region 30 b are formed.

A sidewall insulation film 32 is formed on the side wall of the gate electrode 26.

In the semiconductor substrate 10 on both side of the sidewall insulation film 32 formed on the side wall of the gate electrode 26, a heavily doped region 34, specifically a heavily doped source region 34 a and heavily doped drain region 34 b are formed. The lightly doped source region 30 a and a heavily doped source region 34 a form a source region 36 a. The lightly doped drain region 30 b and the heavily doped drain region 34 b form a drain region 36 b.

A sidewall insulation film 38 is further formed on the side wall of the sidewall insulation film.

A silicide layer 40 a, 40 b is formed respectively on the source region 36 a and the drain region 36 b.

Thus, the transistor 20 in the logic region 16 is constituted.

Next, the transistor 22 formed in the high withstand voltage region 18 will be explained.

A gate electrode 26 is formed on the semiconductor substrate 10 with the gate insulation film 24 b formed therebetween. The gate insulation film 24 b of the transistor 22 in the high withstand voltage region is thicker than the gate insulation film 24 a of the transistor 20 of the logic region. A sidewall insulation film 32 is formed on the side wall of the gate electrode 26.

A lightly-doped source region 42 a and a lightly doped drain region 42 b are formed in the semiconductor substrate 10 on both sides of the gate electrode 26.

A heavily doped region 44, specifically a heavily doped source region 44 a and heavily doped drain region 44 b are formed in the semiconductor substrate 10 on both side of the gate electrode 26 with the sidewall insulation film 32 formed on the side wall of the gate electrode 26. The lightly doped drain region 42 b and the heavily doped drain region 44 b constitute the drain region 45 b.

As shown in FIG. 2B, the heavily doped drain region 44 b is formed in the region of the lightly doped drain region 42 b except the peripheral region thereof. In other words, the heavily doped drain region 44 b is formed, contained by the lightly doped drain region 42 b. The edge of the heavily doped drain region 44 b is spaced from the edge of the lightly doped drain region 42 b, which mitigates the concentration of the electric fields.

The heavily doped source region 44 a is formed at the edge of the lightly doped source region 42 a. In other words, the heavily doped source region 44 a is not contained by the lightly doped source region 42 a.

In the present embodiment, the edge of the heavily doped drain region 44 b is spaced from the edge of the lightly doped drain region 42 b only in the drain region. This is because of the risk that high voltages are applied, which may cause the dielectric breakdown in the drain region. On the other hand, the source region, where high voltages are not applied, is free from the risk of the dielectric breakdown. It is needless to space the edge of the heavily doped source region 44 a from the edge of the lightly doped source region 42 a.

The distance d₁ between the edge of the heavily doped drain region 44 b on the side of the gate electrode 26 and the edge of the lightly doped drain region 42 b on the side of the gate electrode 26 is, e.g., 3 μm. On the other hand, the distance d₂ between the edge of the heavily doped source region 44 a on the side of the gate electrode 26 and the edge of the lightly doped source region 42 a on the side of the gate electrode 26 is, e.g., 0.1 μm. That is, in the present embodiment, the distance d₁ between the edge of the heavily doped drain region on the side of the gate electrode and the edge of the lightly doped drain region on the side of the gate electrode is larger than the distance d₂ between the edge of the heavily doped source region on the side of the gate electrode and the edge of the lightly doped source region on the side of the gate electrode.

In the present embodiment, the distance d₁ between the edge of the heavily doped drain region 44 b on the side of the gate electrode 26 and the edge of the lightly doped drain region 42 b on the side of the gate electrode 26 is 3 μm. However, the distance d₁ is not limited to 3 μm and can be suitably set in accordance with a required withstand voltage.

In the present embodiment, the distance d₂ of the edge of the heavily doped source region 44 a on the side of the gate electrode 26 and the edge of the lightly doped source region 42 a on the side of the gate electrode 26 is 0.1 μm. However, the distance d₂ is not limited to 0.1 μm and can be suitably set in accordance with a required withstand voltage.

In the present embodiment, a reason why the distance d₁ between the edge of the heavily doped drain region 44 b on the side of the gate electrode 26 and the edge of the lightly doped drain region 42 b on the side of the gate electrode 26 is longer than the distance of the edge of the heavily doped source region 44 a on the side of the gate electrode 26 and the edge of the lightly doped source region 42 a on the side of the gate electrode 26 is as follows.

That is, with the distance d₁ between the edge of the heavily doped drain region 44 b on the side of the gate electrode 26 and the edge of the lightly doped drain region 42 b on the side of the gate electrode 26 and the distance d₂ between the edge of heavily doped source region 42 a on the side of the gate electrode 26 and the edge of the lightly doped source region 44 a on the side of the gate electrode are long, which raises the source/drain electric resistance. Not only the distance d₁ between the edge of the heavily doped drain region 44 b on the side of the gate electrode 26 and the edge of the lightly doped drain region 42 b on the side of the gate electrode 26 but also the distance d₂ between the edge of heavily doped source region 44 a on the side of the gate electrode 26 and the edge of the lightly doped source region 42 a on the side of the gate electrode are set long, which much raises the source/drain electric resistance. On the other hand, because high voltages are not applied to the source region, the distance between the edge of the lightly doped source region 42 a on the side of the gate electrode 26 and the edge of the heavily doped source region 44 a on the side of the gate electrode 26, it is needless to set long the distance between the edge of the lightly doped source region 42 a on the side of the gate electrode 26 and the edge of the heavily doped region 44 a on the side of the gate electrode 26. Then, in the present embodiment, the distance d₁ alone between the edge of the lightly doped drain region 42 b on the side of the gate electrode 26 and the edge of the heavily doped drain region 44 b on the side of the gate electrode 26, which is in the drain region, is set long. Thus, according to the present embodiment, the source-drain electric resistance increase of the high withstand voltage transistor 22 is depressed while high withstand voltages can be ensured.

The distance d₃ between the edge of the heavily doped drain region 44 b and the edge of the element isolation region 14 is, e.g., 3 μm. The distance d₃ between the edge of the heavily doped drain region 44 b and the edge of the element isolation region 14 is set to be equal to the distance d₁ between the edge of the heavily doped drain region 44 b on the side of the gate electrode 26 and the edge of the lightly doped drain region 42 b on the side of the gate electrode 26. On the other hand, the edge of the heavily doped source region 44 a is adjacent to the edge of the element isolation region 14. In the present embodiment, the distance d₃ between the heavily doped drain region 44 b and the element isolation region 14 is large so that high withstand voltages of the high withstand voltage transistor 22 can be ensured. On the other hand, high voltages are not applied to the source region, which makes it needless to space the heavily doped source region 44 a and the element isolation region 14 from each other.

In the present embodiment, the distance d₃ between the edge of the heavily doped drain region 44 b and the edge of the element isolation region 14 is set to be 3 μm. The distance d₃ is not limited to 3 μm and can be suitably set in accordance with a required withstand voltages.

A sidewall insulation film 38 is further formed on the sidewall insulation film 32 formed on the gate electrode 26. An insulation film 38 is formed on the semiconductor substrate 10 on the side of the drain. The insulation film 38 functions as a mask for forming a silicide layer 40. The insulation film 38 is formed of one and the same film as the sidewall insulation film 38.

An opening 46 is formed in the insulation film 38 down to the heavily doped drain region 44 b.

Silicide layers 40 c, 40 d are formed on the exposed surface of the semiconductor substrate 10. The silicide layer 40 d is formed only inside the opening 46 in the drain region. As shown in FIG. 2B, the silicide layer 40 d is formed in the region of the heavily doped drain region 44 d except the peripheral part thereof. The distance d₄ between the edge of the silicide layer 40 d on the side of the gate electrode 26 and the edge of the heavily doped drain region 44 b on the side of the gate electrode 26 is, e.g., about 1 μm.

In the present embodiment, the distance d₄ between the edge of the silicide layer 40 d on the side of the gate electrode 26 and the edge of the heavily doped drain region 44 b on the side of the gate electrode 26 is about 1 μm but is not limited to 1 μm. Setting the distance d₄ between the edge of the silicide layer 40 d on the side of the gate electrode 26 and the edge of the heavily doped drain region 44 b on the side of the gate electrode 26 to be 0.1 μm or above can mitigate to some extent the concentration of the electric fields and ensure some high withstand voltages. When the distance d₄ between the edge of the silicide layer 40 d on the side of the gate electrode 26 and the edge of the heavily doped drain region 44 b on the side of the gate electrode 26 to be 0.5 μm or above, the concentration of the electric fields can be further mitigated, and accordingly high withstand voltages can be ensured.

The silicide layer 40 c in the source region is formed on the edge of the heavily doped source region 44 a. This is because it is needless to mitigate the concentration of the electric fields in the source region, to which high voltages are not applied.

Thus, the high withstand voltage transistor 22 is constituted.

An inter-layer insulation film 50 is formed on the entire surface of the semiconductor substrate 10 with the transistors 20, 22 formed on.

Contact holes 52 are formed in the inter-layer insulation film 50 down to the silicide layers 40 a–40 d. Conductor plugs 54 are buried in the contact holes 52. An interconnection layer 56 is formed on the inter-layer insulation film 50 with the conductor plugs 54 buried in.

The conductor plugs 54 are formed in the parts of the silicide layers 40 a–40 d except the peripheral parts. In the drain region of the high withstand voltage transistor 22, the distance d₅ between the edge of the conductor plug 54 and the edge of the silicide layer 40 d is, e.g., 0.3 μm or above. In the present embodiment, the conductor plug 54 is formed down to the part of the silicide layer 40 d except the peripheral part so that in the drain region of the high withstand voltage transistor 22, the concentration of the electric fields can be mitigated, and high withstand voltages can be ensured.

In the source region, to which high voltages are not applied, it is needless to make the distance between the edge of the slicide layer 40 c and the edge of the conductor plug 54 large.

The semiconductor device according to the present embodiment is characterized mainly in that in the drain region of the high withstand voltage transistor 22, the heavily doped drain region 44 b is formed in the part of the lightly doped drain region 42 b except the peripheral part, the silicide layer 40 d is formed in the region of the heavily doped drain region 44 b except the peripheral part, the conductor plug 54 is formed down to the part of the silicide layer 40 d except the peripheral part, and the heavily doped drain region 44 b is spaced from the element isolation region 14.

In said another proposed semiconductor device shown in FIG. 16, the electric fields are concentrated on the drain region of the high withstand voltage transistor, and high withstand voltages cannot be obtained.

In contrast to this, according to the present embodiment, when high voltages are applied to the drain region, which is constituted as described above, the concentration of the electric fields on the drain region can be mitigated. Thus, according to the present embodiment, even with the silicide layer formed on the source/drain region, the withstand voltages in the high withstand voltage transistor can be sufficiently high. Furthermore, according to the present embodiment, the drain region alone has the above-described structure, whereby the increase of the source-drain electric resistance can be prevented while high withstand voltages can be ensured.

The above-described Patent Reference 1 discloses a semiconductor device in which double side wall insulation films are formed, a silicide layer is formed in the heavily doped source/drain region, spaced from the gate electrode, and the conductor plug is formed down to the silicide layer. The semiconductor device disclosed in Patent Reference 1 is largely different from the semiconductor device according to the present embodiment in that in the former, the heavily doped drain region is formed also on the edge of the lightly doped drain region, the silicide layer is formed also on the edge of the heavily doped drain region, and the heavily doped drain region is not spaced from the element isolation region. The semiconductor device described in Patent Reference 1 cannot sufficiently mitigate the concentration of the electric fields in the drain region, and sufficient withstand voltages cannot be ensured.

(The Method for Fabricating the Semiconductor Device)

Next, the method for fabricating the semiconductor device according to the present embodiment will be explained with reference to FIGS. 3A to 14B.

First, as shown in FIG. 3A, a mask 58 is formed respectively in a region 16 n where a logic n-channel transistor to be formed in, a region 16 p where a logic p-channel transistor to be formed in, a region 18 n where an n-channel transistor of a high withstand voltage region, and in a region 18 p where a p-channel transistor of the high withstand voltage region to be formed in. A material of the mask 58 can be, e.g., SiN. The thickness of the mask 58 is, e.g., 120 nm.

Then, as shown in FIG. 3B, a photoresist film 60 is formed on the entire surface by, e.g., spin coating. Then, an opening 62 for opening the region 18 p for the p-channel transistor of the high withstand voltage region is formed by photolithography.

Then, with the photoresist film 60 as a mask, an n type dopant is implanted in the semiconductor substrate 10 by, e.g., ion implantation. As the dopant, P (phosphorus), for example, is used. Conditions for the ion implantation are, e.g., a 180 keV acceleration voltage and a 6×10¹² cm⁻² dose. An n type well 63 is thus formed in the semiconductor substrate 10 in the region 18 p for the p-channel transistor of the high withstand voltage region.

Next, the dopant implanted in then type well 63 is activated by thermal processing.

Then, as shown in FIG. 4A, a photoresist film 64 is formed on the entire surface by, e.g., spin coating. Then, an opening 66 for opening the region 16 p for the p-channel transistor of the logic region to be formed in is formed in the photoresist film 64.

Next, with the photoresist film 64 as a mask, an n type dopant is implanted into the semiconductor substrate 10 by, e.g., ion implantation. The dopant is, e.g., P. Conditions for the ion implantation are, e.g., a 180 keV acceleration voltage and a 1.5×10¹³ cm⁻² dose. An n type well 68 is thus formed in the semiconductor substrate 10 in the region 16 p for the p-channel transistor for the logic region to be formed in.

Then, thermal processing is performed to activate the dopant implanted in the n type well 68.

Next, as shown in FIG. 4B, a photoresist film 70 is formed on the entire surface by, e.g., spin coating. Then, an opening 72 is formed in the photoresist film 70 down to the semiconductor substrate 10 by photolithography. The opening 72 is for forming a channel stop layer 74 of the n-channel transistor 22 n (see FIG. 14B) of the high withstand voltage region.

Then, with the photoresist film 70 as a mask, a p type dopant is implanted into the semiconductor substrate 10 by, e.g., ion implantation. The dopant is, e.g., B (boron). Conditions for the ion implantation are, e.g., a 20 keV acceleration voltage and a 5×10¹⁴ cm⁻² dose. The channel stop layer 74 of the n-channel transistor 22 n of the high withstand voltage region is thus formed.

Next, as shown in FIG. 5A, a photoresist film 76 is formed on the entire surface by, e.g., spin coating. Next, openings 78 are formed in the photoresist film 76 down to the semiconductor substrate 10 by photolithography. The openings 78 are for forming a channel stop layer 80 of the p channel transistor 22 p of the high withstand voltage region (see FIG. 14B).

Then, with the photoresist film 76 as a mask, an n type dopant is implanted into the semiconductor substrate 10 by, e.g., ion implantation. The dopant is, e.g., P. Conditions for the ion implantation are, e.g., a 60 keV acceleration voltage and a 2.5×10¹³ cm⁻² dose. The channel stop layer 80 of the p-channel transistor 22 p of the high withstand voltage region is thus formed.

Next, as shown in FIG. 5B, element isolation regions 14 are formed on the semiconductor substrate 10 by, e.g., LOCOS (LOCal Oxidation of Silicon).

Then, a mask 58 is removed.

Next, a protection film 82 of an SiO₂ film of, e.g., a 15 nm-thickness is formed on the entire surface by, e.g., thermal oxidation.

Then, the protection film 82 is removed by etching the entire surface.

Next, as shown in FIG. 6A, a gate insulation film 24 b of an SiO₂ film of, e.g., a 90 nm-thickness is formed on the entire surface.

Then, the gate insulation film 24 b formed in the regions 16 n, 16 p for the logic transistor to be formed in is removed.

Next, a protection film 84 of an SiO₂ film of, e.g., a 15 nm-thickness is formed on the entire surface.

Then, as shown in FIG. 6B, a photoresist film 86 is formed on the entire surface by, e.g., spin coating. Next, an opening 88 for opening the region 16 n for the n-channel transistor of the logic region to be formed in is formed in the photoresist film 86.

Next, with the photoresist film 86 as a mask, a p type dopant is implanted into the semiconductor substrate 10 by, e.g., ion implantation. The dopant is, e.g., B. Conditions for the ion implantation are, e.g., a 140 keV acceleration energy and a 8×10¹² cm⁻² dose. A p type well 90 is thus formed in the region 16 n for the n-channel transistor of the logic region to be formed in.

Then, with the photoresist film 96 as a mask, a p type dopant is implanted into the semiconductor substrate 10 by, e.g., ion implantation. The dopant is, e.g., B. Conditions for the ion implantation are, e.g., a 30 keV acceleration energy and a 3×10¹² cm⁻² dose. A channel doped layer 92 is formed in the region 16 n for the n-channel transistor of the logic region to be formed in. The channel doped layer 92 is for controlling the threshold voltage.

Next, as shown in FIG. 7A, a photoresist film 94 is formed on the entire surface by, e.g., spin coating. Then, an opening 96 for opening the region 18 n for the n-channel transistor of the high withstand voltage to be formed in is formed in the photoresist film 94 by photolithography.

Then, with the photoresist film 94 as a mask, a p type dopant is implanted into the semiconductor substrate 10 by, e.g., ion implantation. The dopant is, e.g., B. Conditions for the ion implantation are, e.g., 45 keV acceleration energy and a 2×10¹¹ cm⁻² dose. The channel doped layer 98 is thus formed in the region 18 n for the n-channel transistor of the high withstand voltage region to be formed in.

Then, as shown in FIG. 7B, a photoresist film 100 is formed on the entire surface by, e.g., spin coating. Then, an opening 102 for opening the region 18 n for the n-channel transistor of the high withstand voltage region to be formed in is formed in the photoresist film 100.

Next, with the photoresist film 100 as a mask, an n type dopant is implanted into the semiconductor substrate 10 by, e.g., ion implantation. The dopant is, e.g., B. Conditions for the ion implantation are, e.g., a 45 keV acceleration energy and a 8×10¹¹ cm⁻² dose. A channel doped layer 104 is thus formed in the region 18 p for the p-channel transistor of the high withstand voltage region to be formed in.

Then, as shown in FIG. 8A, the protection film 84 formed in the regions 16 n, 16 p for the logic transistor to be formed in is removed.

Then, a gate insulation film 24 a of an SiO₂ film of, e.g., a 7 nm-thickness is formed in the regions 16 n, 16 p for the logic transistor to be formed in.

Then, a 50 nm-thickness doped amorphous silicon film 106 is formed on the entire surface by, e.g., CVD. The amorphous silicon film 106 is for forming the gate electrode 26.

Then, a photoresist film 108 is formed on the entire surface by, e.g., spin coating. Then, an opening 110 for opening the logic region 16 is formed in the photoresist film 108 by photolithography.

Next, with the photoresist film 108 as a mask, a p type dopant is implanted in the semiconductor substrate 10 by, e.g., ion implantation. The dopant is, e.g., B. Conditions for the ion implantation are, e.g., a 30 keV acceleration energy and a 2×10¹² cm⁻² dose. A channel doped layer 112 is thus formed in the logic region 16.

Then, a tungsten silicide film 113 is formed on the amorphous silicon film 106.

Next, a cap film 28 of an SiO₂ film of, e.g., a 45 nm-thickness is formed on the entire surface by CVD.

Then, the cap film 28 is patterned by photolithography.

Next, with the cap film 28 as a mask, the tungsten silicide film 113 and the doped amorphous silicon film 106 are etched. The gate electrode 26 is thus formed of the amorphous silicon film 106 and the tungsten silicide film 113 (see FIG. 8B).

Then, as shown in FIG. 9A, a photoresist film 114 is formed on the entire surface by, e.g., spin coating. Next, an opening 116 for opening the regions 18 p, 18 n for the high withstand voltage transistor to be formed in is formed in the photoresist film 114 by photolithography.

Next, with the photoresist film 114 and the gate electrode 26 of the high withstand voltage transistor region as a mask, the gate insulation film 24 b on both sides of the gate electrode 26 of the high withstand voltage transistor.

Then, as shown in FIG. 9B, a photoresist film 118 is formed on the entire surface by, e.g., spin coating. Then, an opening 120 for opening the region 18 n for the n-channel transistor of the high withstand voltage region is formed in the photoresist film 118 by photolithography.

Next, with the photoresist film 118 and the gate electrode 26 as a mask, an n type dopant is implanted into the semiconductor substrate 10 by, e.g., ion implantation. The dopant is, e.g., P (phosphorus). Conditions for the ion implantation are, e.g., a 60–90 keV acceleration energy and a 3×10¹² cm⁻² dose. A lightly doped source region 42 a and a lightly doped drain region 42 b are thus formed in the semiconductor substrate 10 on both sides of the gate electrode 26.

Then, as shown in FIG. 10A, a photoresist film is formed on the entire surface by, e.g., spin coating. Then, an opening 124 for opening the region 18 p for the p-channel transistor of the high withstand voltage region to be formed in is formed in the photoresist film by photolithography.

Next, with the photoresist film 122 and the gate electrode 26 as a mask, an n type dopant is implanted into the semiconductor substrate 10 by, e.g., ion implantation. The dopant is, e.g., B. Conditions for the ion implantation are, e.g., a 45 keV acceleration energy and a 3×10¹² cm⁻² dose. The lightly doped source region 42 c and the lightly doped drain region 42 d are thus formed in the semiconductor substrate 10 on both sides of the gate electrode 26.

Then, as shown in FIG. 10B, a photoresist film 126 is formed on the entire surface by, e.g., spin coating. Next, an opening 128 for opening the region 16 n for the n-channel transistor of the logic region to be formed in is formed in the photoresist film 126 by photolithography.

Next, with the photoresist film 126 and the gate electrode 26 as a mask, an n type dopant is implanted by, e.g., ion implantation. The dopant is, e.g., P. Conditions for the ion implantation are, e.g., a 20 keV acceleration energy and a 4×10¹³ cm⁻² dose. The lightly doped source region 30 a and the lightly doped drain region 30 b are formed in the semiconductor substrate 10 on both sides of the gate electrode 26.

Then, as shown in FIG. 11A, a photoresist film 130 is formed on the entire surface by, e.g., spin coating. Then, an opening 132 for opening the region 16 p for the p-channel transistor of the logic region to be formed in is formed in the photoresist film 130 by photolithography.

Next, with the photoresist film 130 and the gate electrode 26 as a mask, a p type dopant is implanted by, e.g., ion implantation. The dopant is, e.g., BF₂ ⁺. Conditions for the ion implantation are, e.g., a 20 keV acceleration energy and a 1×10¹³ cm⁻² dose. The lightly doped source region 30 c and the lightly doped drain region 30 d are thus formed in the semiconductor substrate 10 on both sides of the gate electrode 26.

Then, a 120 nm-thickness SiO₂ insulation film is formed by, e.g., CVD. Then, the insulation film is anisotropically etched. The sidewall insulation film 32 is thus formed on the side wall of the gate electrode 26 (see FIG. 11B).

Next, as shown in FIG. 12A, a photoresist film 134 is formed on the entire surface by, e.g., spin coating. Then, openings 136 a–136 c are formed in the photoresist film 134 by photolithography. The opening 136 a is for forming the heavily doped source region 34 c and the heavily doped drain region 34 d of the p-channel transistor 20 p of the logic region. The opening 136 b is for forming the heavily doped source region 44 c of the p-channel transistor 22 p of the high withstand voltage region. The opening 136 c is for forming the heavily doped drain region 44 d of the p-channel transistor 22 p of the high withstand voltage region.

Then, with the photoresist film 134 as a mask, a p type dopant is implanted. The dopant is, e.g., BF₂. Conditions for the ion implantation are, e.g., a 20 keV acceleration voltage and a 3×10¹⁵cm⁻² dose. The heavily doped source region 34 c and the heavily doped drain region 34 d are thus formed in the semiconductor substrate 10 on both sides of the gate electrode 26 in the region 16 p for the p-channel MOS transistor of the logic region. The heavily doped source region 44 c and the heavily doped drain region 44 d are formed in the semiconductor substrate 10 on both sides of the gate electrode 26 in the region 18 p for the p-channel MOS transistor of the high withstand voltage region.

Next, as shown in FIG. 12B, a photoresist film 138 is formed on the entire surface by, e.g., spin coating. Then, openings 140 a, 140 b, 140 c are formed in the photoresist film 138 by photolithography. The photoresist film is thus patterned to cover the peripheral part of the lightly doped drain region 42 d. The opening 140 a is for forming the heavily doped source region 34 a and the heavily doped drain region 34 b of the n-channel transistor 20 n of the logic region. The opening 140 b is for forming the heavily doped source region 44 a of the n-channel transistor of the high withstand voltage region. The opening 140 c is for forming the heavily doped drain region 44 b of the n-channel transistor of the high withstand voltage region.

Then, with the photoresist film 138 and the gate electrode 26 as a mask, an n type dopant is implanted. The dopant is, e.g., As (arsenic). Conditions for the ion implantation are, e.g., a 30 keV acceleration voltage and a 1×10¹⁵ cm⁻² dose. The heavily doped source region 34 a and the heavily doped drain region 34 b are thus formed in the semiconductor substrate 10 on both sides of the gate electrode 26 in the region 16 n for the n-channel transistor of the logic region to be formed in. The heavily doped source region 44 a and the heavily doped drain region 44 b are formed in the semiconductor substrate 10 on both sides of the gate electrode 26.

Next, thermal processing is performed to activate the dopant introduced into the heavily diffused layer.

Then, an insulation film 38 of a 100 nm-thickness SiO₂ film is formed on the entire surface by, e.g., low temperature plasma CVD.

Then, as shown in FIG. 13A, a photoresist film 142 is formed on the entire surface by, e.g., spin coating. Then, openings 144 a–144 d are formed in the photoresist film 142 by photolithography. The photoresist film 142 is thus patterned to cover the peripheral part of the lightly doped drain region 42 b. The opening 144 a is for opening the region 16 for the transistor of the logic region to be formed in and the source-side region of the n-channel transistor 22 n of the high withstand voltage region. The opening 144 b is for opening the source-side region of the p-channel transistor 22 p of the high withstand voltage region. The opening 144 c is for opening the region for the drain-side silicide layer 40 d of the n-channel transistor 22 n of the high withstand voltage region. The opening 144 c is formed with a distance between the edge of the opening 144 c on the side of the gate electrode 26 and the edge of the heavily doped drain region 44 b on the side of the gate electrode 26 made, e.g., 3 μm. The opening 144 d is for opening the region for the drain-side silicide layer 40 h of the p-channel transistor 22 p of the high withstand voltage. The opening 144 d is formed with a distance between the edge of the opening 144 d on the side of the gate electrode 26 and the edge of the heavily doped drain region 44 d on the side of the gate electrode 26 made, e.g., 3 μm.

Then, with the photoresist film 142 as a mask, the insulation film 38 is anisotropically etched. The sidewall insulation film 38 is further formed on the side wall of the gate electrode with the sidewall insulation film 32 formed on. In the drain-side of the transistor 22 n, 22 p of the high withstand voltage region, the sidewall insulation film 38 is left, covering the peripheral parts of the heavily doped drain regions 44 b, 44 d and the lightly doped drain regions 42 b, 42 d. The insulation film 38 left in the drain-side of the transistor 22 n, 22 p of the high withstand voltage region functions as a mask for forming the silicide layer 40 only in a required region of the surface of the semiconductor substrate 10.

Next, as shown in FIG. 13B, the silicide film 40 a–40 h of, e.g., titanium silicide is formed on the exposed surface of the semiconductor substrate 10.

Then, as shown in FIG. 14 a, the inter-layer insulation film 50 of a 700 nm-thickness SiO₂ film is formed on the entire surface by, e.g., CVD.

Next, the contact holes 52 are formed in the inter-layer insulation film 50 down to the silicide film 40. At this time, the contact holes 52 are formed down to the region of the silicide film 40 except the peripheral part thereof.

Then, the conductor plugs 54 are buried in the contact holes 52.

Next, a conductor film of a 500 nm-thickness Al film is formed, e.g., PVD (Physical Vapor Deposition). Then, the conductor film is patterned by photolithography to form the interconnections 56. The interconnections 56 are thus formed, connected to the conductor plugs 54.

Thus, the semiconductor device according to the present embodiment is fabricated.

(Modifications)

Next, modifications of the semiconductor device according to the present embodiment will be explained with reference to FIG. 15. FIG. 15 is a sectional view of the semiconductor device according to the present modification.

The semiconductor device according to the present modification is characterized mainly in that the silicide layer 40 i, 40 j is formed also on the gate electrode 26.

As shown in FIG. 15, in the semiconductor device according to the present modification, the silicide layer 40 i, 40 j is formed on the gate electrode 26. The silicide layer 40 i, 40 j can be formed concurrently with forming the silicide layer 40 a–40 h.

As described above, the silicide layer 40 i, 40 j may be formed also on the gate electrode 26. According to the present modification, the silicide layer 40 i, 40 j, whose electric resistance is low, can decrease the resistance of the gate electrode 26.

[Modifications]

The present invention is not limited to the above-described embodiment and can cover other various modifications.

For example, in the above-described embodiment, the present invention is applied to the semiconductor device having the logic transistors and the transistors of the high withstand voltage transistors mixedly formed. However, the logic transistors and the transistors of the high withstand voltage region are not essentially mixed. The present invention is applicable to, e.g., semiconductor devices having high withstand voltage transistors.

The above-described embodiment uses the structure as described above, that high withstand voltage can be obtained only in the drain region of the high withstand voltage transistor. However, the above-described structure in which high withstand voltage can be obtained also in the source region of the high withstand voltage transistors. However, when the above-described structure, in which high withstand voltages can be obtained also in the source region, is used, the source-drain electric resistance further rises. In terms of making the source-drain electric resistance low, preferably the above-described structure, in which high withstand voltages can be obtained only in the drain region is used. 

1. A method for fabricating a semiconductor device comprising steps of: forming a gate electrode on a semiconductor substrate with a gate insulation film formed therebetween; implanting a dopant into the semiconductor substrate with the gate electrode as a mask to form a lightly doped source region in the semiconductor substrate on one side of the gate electrode and a lightly doped drain region in the semiconductor substrate on the other side of the gate electrode; forming a sidewall insulation film on the side wall of the gate electrode; implanting a dopant into the semiconductor substrate with a first mask covering a peripheral part of the lightly doped drain region, with the gate electrode and the sidewall insulation film as another mask, to form a heavily doped source region in the semiconductor substrate on the one side of the gate electrode and a heavily doped drain region in a region of the lightly doped drain region except a peripheral part of the lightly doped drain region; removing the first mask and forming a second mask covering an entire peripheral part top surface of the heavily doped drain region, wherein the second mask exposing the heavily doped source region and a top portion of the gate electrodes; and forming a first silicide layer on the heavily doped source region and a second silicide layer in a region of the heavily doped drain region except the entire peripheral part top surface of the heavily doped drain region, with the second mask as a mask.
 2. A method for fabricating a semiconductor device according to claim 1, further comprising, after the step of forming the first silicide layer and the second silicide layer, forming a first conductor plug connected to the first silicide layer and a second conductor plug connected to the second silicide layer, and in which in the step of forming the first conductor plug and the second conductor plug, the second conductor plug being formed down to a part of the second silicide layer except a peripheral part of the second silicide layer.
 3. A method for fabricating a semiconductor device according to claim 2, wherein in the step of forming the first conductor plug and the second conductor plug, the first conductor plug is formed down to a part of the first silicide layer except a peripheral part of the first silicide layer.
 4. A method for fabricating a semiconductor device according to claim 2, wherein in the step of forming the first silicide layer and the second silicide layer, a third silicide layer is further formed on the gate electrode. 